Yet another n00b setup question

8 replies [Last post]
julesa
Offline
Joined: 06/17/2008
Points: 16

I'm about 200 pounds, and I commute 20 miles to work each way. There are some hills, but they're not too bad. I can take the hills under my own power, it's just slow. I want to speed up my commute and make the uphill sections faster and easier.

I am considering adding a Roadrunner 4820 to my bike, powered by a Yesu LiFePo4 48V 10Ah battery. From what I read, this battery should take me 10-15 miles without any pedaling at all, and I like pedaling. I am fine pedaling the whole way, I just want to speed things up.

From what I read, this setup should get close to 25MPH... I don't think the gearing on my current bike will let me pedal at that speed. So I'm concerned that if I can't pedal assist for most of the distance, the battery will not last for the full commute. Has anyone tried getting a bigger chain ring so they can pedal assist at higher speeds? Would it make sense to do that?

My other concern is that the motor might add some resistance when the battery runs out, or if I choose to turn the throttle off for long flat sections. Will putting this motor on my bike make it a lot harder to ride when the battery is out of juice? (not counting the extra 25 pounds or so)

Should I consider the 20Ah battery? That seems like it might be overkill for me, and they're not cheap!

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.
dogman
dogman's picture
Offline
Joined: 04/29/2008
Points: 830
Re: Yet another n00b setup question

Yes, a bigger chainring would help you peadal more, and there are lots of other tricks to extend range.

Yes you need the 20 ah to go 20 miles day in and day out. Some batteries will cut out on hills and such if less than 20 ah. If you use less than 80% of the capacity instead of 100% of it you will get more cycles out of the battery, and GREATLY reduce the risk of an overdischarge. This is really important with lithium. The BMS is supposed to prevent this, but it's like parachuting, it better work every time. I'd rather not ask the bms to take action by using less than 100% of the charge. I like a big fudge factor on things.

No you do not want to peadle the unenergized bike. There will be a slighltly noticeable drag from the motor, and a REALLY noticalble extra 50 pounds. Think of a bike with a rebar frame. Not fun unless you like a workout.

20 ah from yesa is expensive, but try ping, I heard he may be back in buisness, having a new way to ship. just email him, his website, pingbattery has the email address. Another newbie just found a good deal at Fox Battery. Those look comparable to the yesas and are pretty good price.

__________________

Be the pack leader.
36 volt sla schwinn beach cruiser
36 volt lifepo4 mongoose mtb
24 volt sla + nicad EV Global

bocabikeguy
Offline
Joined: 06/07/2008
Points: 106
Re: Yet another n00b setup question

If you are going 20 miles to work every day, a 20 Ah battery is not overkill. You will use the bike more if you know you have enough power to make the trip even when you are sick, tired, or otherwise unable to pedal. For an added bonus, the higher amp-hour battery will last much longer.

julesa
Offline
Joined: 06/17/2008
Points: 16
Re: Yet another n00b setup question

julesa wrote:

From what I read, this setup should get close to 25MPH... I don't think the gearing on my current bike will let me pedal at that speed.

Nevermind this point. My highest gear ratio is 44:11, and a 100rpm cadence in that gear should equal around 30mph on my bike. I didn't realize I was going so fast -- no speedometer.

So that brings up the question - what if I want to pedal, or coast, faster than the motor's top speed? Will it assist at all, or could it actually add drag? If it does add significant drag, will it still do so when the system is turned off completely?

Also, would someone please confirm whether a 48v 10Ah LiFePo4 battery should have enough juice to last 20 miles (or within a few miles of that) if I'm pedaling the whole way? Again, there are a couple moderate hills, and I've got about 275 pounds total weight including the bike, motor, battery, cargo, and my big butt. If 10Ah will only take me 12-14 miles with pedal assist, then I will want to upgrade to a 20Ah battery.

I'm completely open to suggestions - if you guys think of another system that would better meet my needs, I'm all ears.

Thank you!!!
-Jules

julesa
Offline
Joined: 06/17/2008
Points: 16
Re: Yet another n00b setup question

bocabikeguy wrote:

If you are going 20 miles to work every day, a 20 Ah battery is not overkill. You will use the bike more if you know you have enough power to make the trip even when you are sick, tired, or otherwise unable to pedal. For an added bonus, the higher amp-hour battery will last much longer.

Good to know it will last longer, thank you!

julesa
Offline
Joined: 06/17/2008
Points: 16
Re: Yet another n00b setup question

Would there be any downside to getting two 10Ah batteries and running them in parallel, over just having a single 20Ah? Would they still last longer than a single 10Ah battery? Seems two 10Ah cost pretty close to the same as one 20Ah at YESA.

chas_stevenson
chas_stevenson's picture
Offline
Joined: 12/06/2006
Points: 1309
Re: Yet another n00b setup question

As I understand these packs 1 - 20AH is the same as 2 - 10AH since each pack is made from the same cells. The 20AH just has twice as many cells as the 10AH. Hope this answers your question.

Grandpa Chas S.

julesa
Offline
Joined: 06/17/2008
Points: 16
Re: Yet another n00b setup question

Thanks, guys. Does anyone have a Crystalyte motor, and if so, do you have any trouble pedaling when the battery runs out?

julesa
Offline
Joined: 06/17/2008
Points: 16
Re: Yet another n00b setup question

dogman:
Weird, your reply was posted at 1:41 pm, but I didn't see it 'till just now... I think you answered all my questions. Thanks very much for the detailed reply!

-Jules

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.
Customize This